In semiconductor manufacturing fabricated electrical devices such as field-effect transistors are connected one to another by fabricated conductive lines, called interconnect lines. It is typical to interpose a vertical interconnect plug between the electrical device and the interconnect lines. This plug is called a contact plug since it is formed to contact the electrical device. The portion of the electrical device contacted by the contact plug is called the contact region. The contact plug may be formed in a hole or cavity called a contact hole. The contact plug provides an electrical coupling of the electrical device and the interconnect lines. In this discussion the contact hole is a channel formed in the semiconductor device and more particularly in a dielectric layer. The channel is formed in order to expose a conductive layer of an electrical device. A contact plug is the object formed in the contact hole when a material fills the contact hole contacting the conductive layer.
In contemporary technology the contact plug is fabricated using tungsten and the interconnect lines are fabricated using aluminum. The use of tungsten necessitates an intricate manufacturing process; one process is utilized for the tungsten deposition and subsequent etch and one process is utilized for the aluminum deposition and subsequent etch. The process is made even more complex by the additional machinery and physical areas needed to perform the distinct processes.
One alternative is the single deposition of aluminum to form the contact plug and interconnect. However step coverage is poor. A conventional laser planarization may be utilized to improve step coverage. The laser planarization comprises subjecting the aluminum to pulses of laser energy. The laser energy imparts thermal energy to the aluminum, liquefying the aluminum and planarizing the surface of the aluminum. When the laser energy is removed the aluminum solidifies. However the solid surface of the aluminum after lasing is rough in areas where laser pulses overlap and has cracks due to the recrystallization which takes place during laser assisted reflow. This aluminum is not suitable for use as interconnect lines because it is difficult to pattern and has low reliability as a conductor. An anti-reflective coating (ARC) may be deposited over the aluminum to help alleviate this problem and improve the process window. The process window is the difference in the optical fluence required for completely filling the contact hole and the optical fluence required to initiate the onset of optical ablation. Although the use of ARC results in a much smoother surface, it typically increases the resistivity of the aluminum since the ARC intermixes with the aluminum forming a composite layer. Since the ARC typically has a higher resistivity than aluminum, the composite layer also has a higher resistivity than aluminum. A higher resistivity is detrimental in the interconnect lines.